What is low AMH?
Anti-Müllerian Hormone, or ‘AMH’ as it is often called, is a hormone which is given off by developing follicles, which are egg sacs containing immature eggs. By measuring this with a blood test, it gives an idea of the state of ovarian reserve and how many eggs are left in the ovaries. This can help determine whether and how urgently treatment is needed, and also how a woman may respond to treatment. AMH naturally decreases with age as the ovarian reserve is depleted, and women in their 40s frequently have low AMH results. AMH levels are considered ‘satisfactory’ if they are above 21.98 pmol/l, although age and other circumstances have to be taken into account in order to make the most accurate assessment. Don’t worry if your AMH levels are below this; there are still treatment options available to you. Here at CREATE there is no cut-off point for AMH or FSH results and we are proud to give every woman a chance.
What causes low AMH?
AMH levels are determined by the number of developing follicles in your ovaries. The most important determining factor in the number of follicles is age, as ovarian reserve diminishes over time. Ovarian reserve begins to decline in the mid to late 30s, and AMH (and hence ovarian reserve) levels tend to be low in women in their 40s.
Age is not always a factor in low AMH however. Some women continue to have high AMH levels into their 40s, while others have declining AMH levels in their 20s or 30s. This can be due to environmental factors such as cancer treatment, or down to inherited genetic causes. It is important to find out the age of menopause in your family because this is often a good guide to the rate of your own fertility decline.
How does low AMH affect fertility?
Low AMH is not a cause of infertility, but it is an indication of a decreased egg reserve. When there are fewer developing eggs in the ovaries, the chance of a mature and healthy egg being released and fertilised decreases. In age-related low AMH, the quality of the eggs may also be affected, as eggs accumulate mutations over time. This may mean that the chances of abnormal fertilisation and miscarriage are increased.
Symptoms and diagnosis
Having low AMH does not necessarily present with obvious symptoms, but some women notice a reduction or absence of periods.
Getting a blood test is the best way of assessing your AMH level.
High FSH and its relationship with ovarian reserve
Low AMH results generally coincide with high FSH results, and both of these together are an indicator of low ovarian reserve. FSH stands for ‘follicle stimulating hormone’, and is a hormone released by the brain which stimulates the growth and development of follicles within the ovaries. Developing follicles release oestrogen which inhibits FSH, indicating that there are enough viable follicles being ‘recruited’. When ovarian reserve is low there will not be many follicles recruited, and the levels of oestrogen released will be low. This gives the brain a signal that not enough follicles are developing, and it will subsequently release more FSH. This is why women with a diminished ovarian reserve will have high FSH levels when this is tested on day 3 of the cycle. FSH used to be the most common blood test used to assess ovarian reserve. However, due to the fact that levels can vary from month to month, we now prefer to test AMH results for a more accurate insight into ovarian reserve.